Cervical cancer is the second leading cause of cancer death in women and there are an estimated 529,000 new cases of cervical cancer and 275,000 deaths per year. In 2013, an estimated 12,340 new cases of invasive cervical cancer are expected to be diagnosed. In turn, the number of agents for the treatment of cervical cancer approved by the Food and Drug Administration (FDA) is very low, even with a dwindling trend over the past decade, (www.cancer.gov), demonstrating an urgent need for the development of new classes of compounds for treating cervical cancer. This need is accentuated by the predicted rise in cases of cervical cancer captured by improved screening and diagnostics, yielding an increase ranging from a few percent to 10% in all facets and stages of cervical cancer (www.bccresearch.com). This situation will not be alleviated by the ongoing anti-HPV vaccine trials, as the results of these will be seen only after several decades.
The main risk factor in cervical cancer is the oncogenic Human Papilloma Virus (HPV). The mechanisms through which HPV interferes with the normal life cycle of infected epithelial cells vary profoundly between high- and low-risk genotypes. In the case of high-risk genotypes, the late-expressed viral E6 oncoprotein is thought to bind specifically to the proteins coded by a couple of genes (p53 and the retinoblastoma tumor suppressor gene), which play a major role in the regulation of the cell cycle.
High-risk E6 also activates telomerase which prevents the erosion of telomeres and allows the host cell to continue through many rounds of division without damage to the DNA. E6 has also been reported to activate nuclear factor kappa B (NF-κB) leading to enhanced expression of Inhibitor of apoptosis protein 2 (IAP2) in HPV16 E6-immortalized human oral keratinocytes and primary human airway epithelial cells. It has also been observed that depletion of c-IAP2 leads to cell death, suggesting that HPV16-induced c-IAP2 expression is necessary for maintenance of the immortalized phenotype.
The E7 oncoprotein has also been implicated in HPV-mediated cancers. The E7 oncoprotein interacts with the cell cycle regulator pRb, inducing its proteolytic degradation, thereby preventing its binding to and inhibiting of the cell cycle promoting transcription factor E2F, with consequent stimulatory effect on cell cycle progression. In addition, E7 stimulates the expression of the S-phase cyclins, E and A, interacts with cyclin-kinase complexes, and abrogates the inhibitory activities of CKIs, such as p21Cip and p27Kip.
Therefore, blocking the activity of E6 and E7 oncoproteins serves as a prime therapeutic target in HPV-mediated cancers. Apart from cervical cancer, there is mounting evidence of HPV as a key causative agent in a number of other important cancers, including oral cancer, various head & neck cancers, as well as anogenital cancers. The established association of the E6 and E7 oncoproteins with many major types of cancer underscores the demand to find targeted treatments against these viral oncoproteins.
There are only 3 drugs (Bleomycin, Cisplatin and Hycamtin) that are approved by FDA against cervical cancer, all of which are known for poor specificity and serious side-effects (www.cancer.gov).
In terms of long-term cure of HPV-mediated cancers, vaccines provide a valid strategy. There are two vaccines (Gardasil and Cervarix) licensed and have been in the market (www.cancer.gov). These vaccines are efficient in preventing infection and, therefore, disease, but it will take decades before their real benefits are revealed and the vaccination coverage is restricted only to a number of well-developed countries. Patients not vaccinated who are already suffering from HPV-mediated cancers or who will still develop cancers, will have urgent needs for more efficient anti-cancer drugs. Due to recent misfortunes in the vaccine industry, the public acceptance for vaccination may also be rather variable. The vaccines will not have 100% penetrance, as they target do not cover all cancer-mediating HPVs.
Therefore, only a partial protection against cancer can be expected. Finally, these vaccines are expensive and will not be affordable for the public health management in all countries, especially not in developing countries. All of these aspects warrant an acute need for implementation of novel and affordable strategies to treat HPV-mediated cancers in the post vaccine era.
WO 2014/033366 discloses the use of anisomelic acid, a diterpenoid isolated from Anisomeles malabarica (L.) R. Br., for anti-viral cancer treatment. In WO 2014/033366, it is shown that anisomelic acid exhibits good efficiency in inducing apoptosis in HPV16 positive cervical cancer cells. Anisomelic acid inhibits protein level expression of E6 and E7, and thus is capable of acting as an anti-HPV agent.
Anisomelic acid is a hydrophobic compound which dissolves in DMSO and hot ethanol, and is mostly insoluble in water or other aqueous solvents. Low aqueous solubility of a drug may be a concern as it leads to poor bioavailability, high intrasubject/intersubject variability and lack of dose proportionality. To address that matter, WO2014/033366 discloses various approaches for achieving successful delivery of anisomelic acid containing drugs orally, such as solid dispersions, anti-solvents, complexation with cyclodextrin and lipid-based formulations, including lipid-based emulsion delivery systems, such as self-microemulsifying drug delivery systems (SMEDDS).
Another concern which relates to any natural substances is that synthesis of the molecules for the purpose of industrial-scale manufacture typically requires multistep processes with a number of separation and purification stages which influence the yield.